This invention relates generally to hydrogel products and their methods of production, and more specifically to adhesive hydrogel sheet products, such as moist wound dressings and electrodes, and to a unique extrusion process for producing such products.
The prior art is replete with disclosures of hydrogel products having numerous applications, including uses as an electrode and as a moist wound dressing.
U.S. Pat. No. 4,989,607, issued to Keusch et al., discloses highly conductive, non-stringy adhesive hydrophilic gels and medical electrodes assemblies manufactured from them. These products include, as the principal water-soluble polymer component, poly(vinyl pyrrolidone), and the products are cross-linked by radiation to provide the desired non-stringy property thereto.
U.S. Pat. No. 5,143,071, issued to Keusch et al., discloses hydrophilic gels and a variety of different products including such gels, including electrodes and moist wound dressings. These products include, as the principal water-soluble polymer component, either poly(vinyl pyrrolidone) or poly(ethylene oxide). As in the Keusch et al. "607 patent discussed above, the products disclosed in the "071 patent are cross-linked by radiation to provide the desired non-stringy property thereto.
In both the Keusch et al. "607 patent and "071 patent the principal water-soluble polymer, i.e., poly(vinylpyrrolidone) or poly(ethylene oxide), is formed into a viscous gel, by the addition of water thereto, prior to being extruded as part of the production process. These water-soluble polymers are not extrudable in a dry state.
U.S. Pat. No. 4,307,717, issued to Hymes et al., discloses a sterile bandage containing a medicament. This bandage has a backing member 11 and a self-adhesive substrate 12 having both a solid phase and a liquid phase. Hymes et al. disclose that virtually all (if not all) of the known water soluble polymers can be utilized in forming the substrate 12 with an added medication, but does not disclose any particular fabrication process. Example 7 discloses a product employing hydroxypropylcellulose (sold under the trademark KLUCEL by Hercules Incorporated of Wilmington, Delaware), a thermoplastic, water-soluble polymer, as approximately 1/6th of the water-soluble polymeric substances in the composition. It is applicant's understanding and belief that the gel identified in Example 7, as well as in the other examples, is formed by a batch process in which water simply is added to the "gelant", and the medication is included in, or goes into the mixture.
U.S. Pat. No. 4,372,311, issued to Potts, discloses non-gel compositions formed by taking a film of poly(ethylene oxide) containing 40 weight percent of calcium carbonate in suspension, presumably formed by solution casting, and then coating said film with an organic solvent solution of one of various "slow-degrading" water resistant polymers Example 9 specifically describes a 20 mil thick KLUCEL sheet coated with a polycaprolactone solution, the product being a non-gel formulation. U.S. Pat. No. 4,650,817, issued to Allen Jr. et al., discloses a breathable, conformable, polymeric adhesive composition which is formed in-situ, and which includes a self-sustaining pressure sensitive adhesive and a hydrophilic filler. The product is a non-gel product. In this patent KLUCEL HF is described as one of a number of water-soluble polymers which can be employed for conferring hydrophilic properties to the disclosed adhesive products. U.S. Pat. No. 4,675,009, issued to Hymes et al., discloses essentially the same compositions as the above-identified Hymes et al. "717 patent, but in transdermal delivery devices.
U.S. Pat. No. 4,684,558, issued to Keusch et al., discloses hydrogel sheets wherein the principal water-soluble polymer therein is poly(ethylene oxide), and wherein radiation treatment of the gel is employed to promote cross-linking.
U.S. Pat. Nos. 4,706,680 and 4,777,954, both issued to Keusch et al., disclose medical electrodes employing a hydrophilic gel, wherein the principal water-soluble polymer therein is poly(ethylene oxide).
U.S. Pat. No. 4,699,146, issued to Sieverding, discloses a conductive, water-soluble, hydrophilic pressure sensitive adhesive comprising a gel of poly(vinylpyrrolidone), cross-linked with ionizing radiation.
European Application Serial No. 83305770.6 (Publication No. 0107376), to Johnson and Johnson, discloses an absorbent dressing comprising a layer of a cross-linked poly(vinylpyrrolidone) gel which is cross-linked by means of ionizing radiation.
None of the above-discussed prior art documents, or for that matter any other prior art known to applicant, discloses or suggests the formation of a hydrogel sheet in which the principal water-soluble polymer is a thermoplastic material which is extruded in a dry state to form a hydrogel product having the desirable attributes (as will be hereinafter discussed) of the hydrogel products of the present invention.